Neutrino

Neutrinos are elementary particles which belong to the lepton family of particles. They have very small masses, and hence travel at close to the speed of light.
Although they interact very rarely, a starship's sensor array contains instruments capable of detecting them.

The presence of elevated neutrinos may indicate the presence of a ship – possibly cloaked. The Bajoran wormhole also emitted neutrinos before opening, giving Deep Space 9 a moment to prepare before any ship came through.

In September 2011, the OPERA collaboration released calculations showing velocities of 17 GeV and 28 GeV neutrinos exceeding the speed of light in their experiments.
On July 12, 2012 OPERA updated their paper by including the new sources of errors in their calculations

When Wesley Crusher returned from Starfleet Academy to visit the Enterprise and met Robin Lefler, he was so distracted that she had to remind him that his "neutrinos are drifting" as he tried to recalibrate the ship's scanners. (TNG: "The Game")

When a shuttlecraft belonging to the J'naii had disappeared into an area of "null space," Data was surprised to detect a neutrino emission (such as a shuttlecraft might emit) apparently coming from nowhere. William Riker later confirmed that the emission was coming from within the null space. (TNG: "The Outcast")

Geordi La Forge attempted to infuse a reactor on Tagra IV with neutrinos when it started to overload. (TNG: "True Q")

In 2370, Martus Mazur's probability-altering gambling machines caused more than eighty percent of solar neutrinos in Deep Space 9 to spin clockwise. Jadzia Dax noticed that most of the neutrinos on Deep Space 9 were spinning in the same direction, when really the direction of a neutrino's spin should have been random. (DS9: "Rivals")

In reality, neutrinos always have a left-handed spin, while antineutrinos always have a right-handed spin, meaning that she probably considers both to be neutrinos.

Jadzia Dax noticed that certain interference in a ship's transponder signal just before it exploded could have been caused by a forced neutrino inversion, such as the Romulans used in their explosives. (DS9: "Improbable Cause")

Seven of Nine found suspiciously erratic neutrino levels while examining the deceptive living cloud, which was posing as a wormhole leading back to the Alpha Quadrant. This was dismissed by the mind-controlled Janeway. (VOY: "Bliss")

Icheb designed a high-resolution gravimetric sensor array that scanned for the neutrino flux associated with wormholes to help Voyager get home faster for his science fair project. He got the idea from studying Starfleet records on the Bajoran wormhole. (VOY: "Child's Play")